Herbicidal esters of 2-bromo-4-methylimidazole-5-carboxylic acid

ABSTRACT

A herbicidal compound having the structural formula ##STR1## wherein R is C 1  -C 10  alkyl, C 3  -C 8  cycloalkyl, C 3  -C 8  cycloalkylalkyl wherein the alkyl has 1 to 6 carbon atoms, C 3  -C 10  alkenyl, C 5  -C 8  cycloalkenyl; benzyl or mono- or di-substituted benzyl wherein the substituents are C 1  -C 4  alkyl, halogen, nitro or C 1  -C 4  haloalkyl; R 1  and R 2  independently are C 1  -C 6  alkyl or aryl, or R 1  and R 2  together form a ring with the nitrogen to which they are attached having 3-8 carbon atoms, optionally substituted with one or two methyl groups.

BACKGROUND OF THE INVENTION

Compounds having the structural formula ##STR2## wherein R is hydrogen,alkyl or substituted alkyl and Y is hydrogen, alkyl, substituted alkyl,halogen, cyano or nitro are described in U.S. Pat. No. 3,501,286 asbeing herbicides.

A compound of the formula ##STR3## is taught by Pyman and Timmis, J.Chem. Soc., pp. 494-498 (1923). However, no utility for this compound istaught other than its use as an intermediate in the preparation ofpharmaceuticals.

DESCRIPTION OF THE INVENTION

This invention relates to esters of2-bromo-4-methylimidazole-5-carboxylic acid as herbicides. The novelcompounds of this invention have the following structural formula (A)##STR4## wherein R is C₁ -C₁₀ alkyl, preferably C₃ -C₆ alkyl, morepreferably C₃ -C₅ alkyl, most preferably isopropyl, isobutyl, isopentyl,or sec-pentyl; C₃ -C₈ cycloalkyl, preferably C₄ -C₆ cycloalkyl, morepreferably cyclopentyl or cyclohexyl; C₃ -C₈ cycloalkylalkyl wherein thealkyl has 1 to 6 carbon atoms, preferably cyclopropylmethyl orcyclopentylmethyl; C₃ -C₁₀ alkenyl, preferably allyl or2-methyl-3-butenyl-1; C₅ -C₈ cycloalkenylbenzyl or mono- ordi-substituted benzyl wherein the substituents are C₁ -C₄ alkyl,halogen, nitro or C₁ -C₄ haloalkyl; R¹ and R² independently are C₁ -C₆alkyl, preferably C₁ -C₄ alkyl, aryl, preferably phenyl; or R¹ and R²together form a ring with the nitrogen to which they are attached,having 3-8 carbon atoms, optionally substituted with one or two methylgroups. Suitable compounds within the above genus are those wherein R isC₃ -C₅ alkyl, R¹ is C₁ -C₄ alkyl and R² is C₁ -C₄ alkyl.

Structural formula A is intended to define compounds of either of thefollowing two structural isomers: ##STR5## or mixtures of the twoisomers in any proportion.

Both isomers are herbicidally active.

In the above description of the compounds of this invention alkylincludes both straight and branched configurations; for example, methyl,ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, andtert-butyl, the amyls, the hexyls, the heptyls, the nonyls and thedecyls.

The compounds of this invention ae active herbicides of a general type.That is, they are herbicidally effective against a wide range of plantspecies. The method of controlling undesirable vegetation of the presentinvention comprises applying an herbicidally effective amount of theabove-described compounds to the area where control is desired.

The compounds of the present invention can be prepared by the followinggeneral method. ##STR6## wherein R is as defined. and TEC is atransesterification catalyst such as Ti(O-alkyl)₄, preferablyTi(isopropoxy)₄. ##STR7## wherein R, R¹ and R² are as defined, and X ischlorine.

Generally, for step (1) at least one mole of the alcohol is used for thereaction with the ethyl ester to prepare the imidazoles. Preferably, aslight mole excess of the alcohol is used. The reaction mixture isrefluxed until completion of the reaction. The reaction product isrecovered by removing the volatile materials. Atmospheric,subatmospheric or superatmospheric pressures can be used, depending onthe boiling point of the solvent used. Ethanol is conveniently strippedat elevated temperatures and reduced pressure.

Reaction step (2) is run in a solvent such as tetrahydrofuran, at atemperature of about 25°, preferably room temperature, using equal moleamounts of the two reactants and a hydride base. Preferably, the hydridebase is sodium hydride.

The reaction product is a mixture of (1) and (3) isomers and is workedup by conventional techniques.

The following example teaches the synthesis of a representative compoundof this invention.

EXAMPLE I Isopropyl ester of 2-Bromo-4-methyl-5-imidazolecarboxylic acid##STR8##

To a suspension of 6.4 grams (g) (2.7×10⁻² moles) ofethyl-2-bromo-4-methyl-5-imidazole carboxylate in 70 milliliters (ml) ofisopropanol was added 0.6 ml (2.4×10⁻³ moles) tetraisopropyl titanate.The resulting mixture was heated to reflux for 3 days, then concentratedin vacuo to one-half the original volume. The solution was cooled on iceand the precipitated crystalline solid was filtered and air dried togive 3.5 g of the desired product, m.p. 193°-194° C.

EXAMPLE II Ethyl Ester of 1- and3-N,N-dimethylformamyl-2-bromo-4-methyl-5-imidazolecarboxylic acid##STR9##

To a suspension of 257 milligrams (mg) (1.07×10⁻² moles) of sodiumhydride in 20 ml of anhydrous tetrahydrofuran was added, in portions,2.0 g (8.58×10⁻³ moles) of ethyl ester of2-bromo-4-methyl-5-imidazolecarboxylate. The resulting suspension wascooled to 0° C. and 866 ml (8.58×10⁻³ moles) of dimethylcarbamylchloride was added by drop. The reaction mixture was stirred overnightat room temperature. The precipitated sodium chloride was removed byfiltration and concentration of the filtrate in vacuo gave 2.4 g (96%)of the desired products, ethyl ester of 1- and3-N,N-dimethylformamyl-2-bromo-4-methyl-5-imidazolecarboxylic acid as ayellow oil.

The following is a table of certain selected compounds that arepreparable according to the procedure described herein. Compound numbersassigned to each compound are used throughout the remainder of theapplication.

                  TABLE I                                                         ______________________________________                                         ##STR10##                                                                    Compound                           n.sub.D.sup.25                             Number  R         R.sup.1   R.sup.2                                                                              or m.p. °C.                         ______________________________________                                        1       ethyl     ethyl     ethyl  yellow oil                                 .sup. 2.sup.a                                                                         ethyl     methyl    methyl yellow oil                                 3       isopropyl methyl    methyl colorless oil                              4       isopropyl isobutyl  isobutyl                                                                             colorless oil                              5       isopropyl butylene       colorless oil                                6       isopropyl ethyl     ethyl  yellowless oil                             7       isopropyl methyl    phenyl yellowless oil                             ______________________________________                                         .sup.a Prepared in Example II.                                           

Herbicidal Screening Tests

As previously mentioned, the herein described compounds produced in theabove-described manner are phytotoxic compounds which are useful andvaluable in controlling various plant species. Selected compounds ofthis invention were tested as herbicides in the following manner.

Pre-emergence herbicide test. On the day preceding treatment, seeds ofeight different weed species are planted in loamy sand soil inindividual rows using one species per row across the width of a flat.The seeds used are green foxtail (FT) (Setaria viridis), watergrass (WG)(Echinochloa crusgalli), wild oat (WO) (Avena fatua), annualmorningglory (AMG) (Ipomoea lacunosa), velvetleaf (VL) (Abutilontheophrasti), Indian mustard (MD) (Brassica juncea), curly dock (CD)(Rumex crispus), and yellow nutsedge (YNG) (Cyperus esculentus). Ampleseeds are planted to give about 20 to 40 seedlings per row, afteremergence, depending upon the size of the plants.

Using an analytical balance, 600 milligrams (mg) of the compound to betested are weighed out on a piece of glassine weighing paper. The paperand compound are placed in a 60 milliliter (ml) wide-mouth clear bottleand dissolved in 45 ml of acetone or substituted solvent. Eighteen ml ofthis solution are transferred to a 60 ml wide-mouth clear bottle anddiluted with 22 ml of a water and acetone mixture (19:1) containingenough polyoxyethylene sorbitan monolaurate emulsifier to give a finalsolution of 0.5% (v/v). The solution is then sprayed on a seeded flat ona linear spray table calibrated to deliver 80 gallons per acre (748L/ha). The application rate is 4 lb/acre (4.48 Kg/ha).

After treatment, the flats are placed in the greenhouse at a temperatureof 70° to 80° F. and watered by sprinkling. Two weeks after treatment,the degree of injury or control is determined by comparison withuntreated check plants of the same age. The injury rating from 0 to 100%is recorded for each species as percent control with 0% representing noinjury and 100% representing complete control.

The results of the tests are shown in the following Table II.

                  TABLE II                                                        ______________________________________                                        Pre-Emergence Herbicidal Activity                                             Application Rate-4.48 kg/ha                                                   Cmpd.                                                                         No.   FT     WG     WO   AMG    VL   MD   CD   YNG                            ______________________________________                                        1      0      0      0    0      0    0    0   0                              2      0      0      0    0      0    0    0   0                              3     100     90    60    90    100  100  100  0                              4      0      0     20    60     60   40   90  0                              5      90     80    60    80    100  100  100  0                              6     100    100    75   100    100  100  100  0                              7     100    100    50   100     10  100   85  0                              ______________________________________                                    

Post-Emergence Herbicide Test: This test is conducted in an identicalmanner to the testing procedure for the pre-emergence herbicide test,except the seeds of the eight different weed species are planted 10-12days before treatment. Also, watering of the treated flats is confinedto the soil surface and not to the foliage of the sprouted plants.

The results of the post-emergence herbicide test are reported in TableIII.

                  TABLE III                                                       ______________________________________                                        Post-Emergence Herbicidal Activity                                            Application Rate-4.48 kg/ha                                                   Cmpd.                                                                         No.   FT     WG     WO   AMG    VL   MD   CD   YNG                            ______________________________________                                        1      80     20     10   20     10   40   90  0                              2      60     40     10   50     60   40  100  0                              3     100    100    100  100    100  100  100  0                              4      90     70     95  100    100  100   90  0                              5     100    100     70  100    100  100  100  0                              6     100     95    100  100    100  100   60  0                              7     100    100    100  100    100  100  100  --                             ______________________________________                                         - = Not tested.                                                          

The compounds of the present invention are useful as herbicides, and canbe applied in a variety of ways at various concentrations. In practice,the compounds herein defined are formulated into herbicidalcompositions, by admixture, in herbicidally effective amounts, with theadjuvants and carriers normally employed for facilitating the dispersionof active ingredients for agricultural applications, recognizing thefact that the formulation and mode of application of a toxicant mayaffect the activity of the materials in a given application. Thus, theseactive herbicidal compounds may be formulated as granules of relativelylarge particle size, as wettable powders, as emulsifiable concentrates,as powdery dusts, as solutions or as any of several other known types offormulations, depending upon the desired mode of application. Preferredformulations for pre-emergence herbicidal applications are wettablepowders, emulsifiable concentrates and granules. These formulations maycontain as little as about 0.5% to as much as about 95% or more byweight of active ingredient. A herbicidally effective amount dependsupon the nature of the seeds or plants to be controlled and the rate ofapplication varies from about 0.05 to approximately 25 pounds per acre,preferably from about 0.1 to about 10 pounds per acre.

Wettable powders are in the form of finely divided particles whichdisperse readily in water or other dispersants. The wettable powder isultimately applied to the soil either as a dry dust or as a dispersionin water or other liquid. Typical carriers for wettable powders includefuller's earth, kaolin clays, silicas and other readily wet organic orinorganic diluents. Wettable powders normally are prepared to containabout 5% to about 95% of the active ingredient and usually also containa small amount of wetting, dispersing, or emulsifying agent tofacilitate wetting and dispersion.

Emulsifiable concentrates are homogeneous liquid compositions which aredispersible in water or other dispersant, and may consist entirely ofthe active compound with a liquid or solid emulsifying agent, or mayalso contain a liquid carrier, such as xylene, heavy aromatic naphtha,isophorone and other non-volatile organic solvents. For herbicidalapplication, these concentrates are dispersed in water or other liquidcarrier and normally applied as a spray to the area to be treated. Thepercentage by weight of the essential active ingredient may varyaccording to the manner in which the composition is to be applied, butin general comprises about 0.5% to 95% of active ingredient by weight ofthe herbicidal composition.

Granular formulations wherein the toxicant is carried on relativelycoarse particles, are usually applied without dilution to the area inwhich suppression of vegetation is desired. Typical carriers forgranular formulations include sand, fuller's earth, bentonite clays,vermiculite, perlite and other organic or inorganic materials whichabsorb or which may be coated with the toxicant. Granular formulationsnormally are prepared to contain about 5% to about 25% of activeingredients which may include surface-active agents such as wettingagents, dispersing agents or emulsifiers; oil such as heavy aromaticnaphthas, kerosene or the petroleum fractions, or vegetable oils; and/orstickers such as dextrins, glue or synthetic resins.

Typical wetting, dispersing or emulsifying agents used in agriculturalformulations include, for example, the alkyl and alkylaryl sulfonatesand sulfates and their sodium salts; polyhydroxy alcohols; and othertypes of surface-active agents, many of which are available in commerce.The surface-active agent, when used, normally comprises from 0.1% to 15%by weight of the herbicidal composition.

Dusts, which are free-flowing admixtures of the active ingredient withfinely divided solids such as talc, clays, flours and other organic andinorganic solids which act as dispersants and carriers for the toxicant,are useful formulations for soil-incorporating application.

Pastes, which are homogeneous suspensions of a finely divided solidtoxicant in a liquid carrier such as water or oil, are employed forspecific purposes. These formulations normally contain about 5% to about95% of active ingredient by weight, and may also contain small amountsof a wetting, dispersing or emulsifying agent to facilitate dispersion.For application, the pastes are normally diluted and applied as a sprayto the area to be affected.

Other useful formulations for herbicidal applications include simplesolutions of the active ingredient in a dispersant in which it iscompletely soluble at the desired concentration, such as acetone,alkylated naphthalenes, xylene and other organic solvents. Pressurizedsprays, typically aerosols, wherein the active ingredient is dispersedin finely-divided form as a result of vaporization of a low boilingdispersant solvent carrier, such as the Freons, may also be used.

The phytotoxic compositions of this invention are applied to the plantsin the conventional manner. Thus, the dust and liquid compositions canbe applied to the plant by the use of power-dusters, boom and handsprayers and spray dusters. The compositions can also be applied fromairplanes as a dust or a spray because they are effective in very lowdosages. In order to modify or control growth of germinating seeds oremerging seedlings, as a typical example, the dust and liquidcompositions are applied to the soil according to conventional methodsand are distributed in the soil to a depth of at least 1/2 inch belowthe soil surface. It is not necessary that the phytotoxic compositionsbe admixed with the soil particles since these compositions can also beapplied merely by spraying or sprinkling the surface of the soil. Thephytotoxic compositions of this invention can also be applied byaddition to irrigation water supplied to the field to be treated. Thismethod of application permits the penetration of the compositions intothe soil as the water is absorbed therein. Dust compositions, granularcompositions or liquid formulations applied to the surface of the soilcan be distributed below the surface of the soil by conventional meanssuch as discing, dragging or mixing operations.

The phytotoxic compositions of this invention can also contain otheradditaments, for example, fertilizers and other herbicides, pesticidesand the like, used as adjuvant or in combination with any of theabove-described adjuvants. Other phytotoxic compounds useful incombination with the above-described compounds include, for example,2,4-dichlorophenoxyacetic acids, 2,4,5-trichlorophenoxyacetic acid,2-methyl-4-chlorophenoxyacetic acid and the salts, esters and amidesthereof, triazine derivatives, such as2,4-bis(3-methoxypropylamino)-6-methylthio-s-triazine,2-chloro-4-ethylamino-6-isopropylamino-s-triazine, and2-ethylamino-4-isopropyl-amino-6-methyl-mercapto-s-triazine; ureaderivatives, such as 3-(3,5-dichlorophenyl)-1,1-dimethylurea and3-(p-chlorophenyl)-1,1-dimethylurea; and acetamides such asN,N-diallyl-α-chloroacetamide, and the like; benzoic acids such as3-amino-2,5-dichlorobenzoic acid; thiocarbamates such as S-propylN,N-dipropylthiocarbamate, S-ethyl N,N-dipropylthiocarbamate, S-ethylcyclohexylthiocarbamate, S-ethyl hexahydro-1H-azepine-1-carbothioate andthe like; anilines such as4-(methylsulfonyl)-2,6-dinitro-N,N-substituted aniline,4-trifluoromethyl-2,6-dinitro-N,N-di-n-propyl aniline,4-trifluoromethyl-2,6-dinitro-Nethyl-N-butyl aniline,2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid,2-[1-(ethoxyimino)butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one,(±)-butyl- 2-[4-[(5-trifluoromethyl)-2-pyridinyl)oxy]phenoxy]propanate,sodium 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate,3-isopropyl-1H-2,1,3-benzothiadiazine-4(3H)-one-2,2-dioxide, and4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5-(4H)-one or(4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one).Fertilizers useful in combination with the active ingredients include,for example, ammonium nitrate, urea and superphosphate. Other usefuladditaments include materials in which plant organisms take root andgrow such as compost, manure, humus, sand, and the like.

We claim:
 1. A compound having the structural formula ##STR11## whereinR is C₁ -C₁₀ alkyl, C₃ -C₈ cycloalkyl, C₃ -C₈ cycloalkylalkyl whereinthe alkyl has 1 to 6 carbon atoms, C₃ -C₁₀ alkenyl, C₅ -C₈ cycloalkenyl;benzyl or mono- or di-substituted benzyl wherein the substituents are C₁-C₄ alkyl, halogen, nitro or C₁ -C₄ haloalkyl; R¹ and R² independentlyare C₁ -C₆ alkyl or phenyl, or R¹ and R² together form a saturated ringwith the nitrogen to which they are attached having 3-8 carbon atoms,optionally substituted with one or two methyl groups.
 2. The compound ofclaim 1 wherein R is C₃ -C₅ alkyl, R¹ is C₁ -C₄ alkyl and R² is C₁ -C₄alkyl.
 3. The compound of claim 1 wherein R is isopropyl, R¹ is methyland R² is methyl.
 4. The compound of claim 1 wherein R is isopropyl, R¹is isobutyl and R² is isobutyl.
 5. The compound of claim 1 wherein R isisopropyl, R¹ is ethyl and R² is ethyl.
 6. The compound of claim 1wherein R is isopropyl, and R¹ and R² together are butylene.
 7. Thecompound of claim 1 wherein R is isopropyl, R¹ is methyl and R¹ isphenyl.
 8. The method of controlling undesirable vegetation comprisingapplying to the area where control is desired an herbicidally effectiveamount of a compound having the structural formula ##STR12## wherein Ris C₁ -C₁₀ alkyl, C₃ -C₈ cycloalkyl, C₃ -C₈ cycloalkylalkyl wherein thealkyl has 1 to 6 carbon atoms, C₃ -C₁₀ alkenyl, C₅ -C₈ cycloalkenyl;benzyl or mono- or di-substituted benzyl wherein the substituents are C₁-C₄ alkyl, halogen, nitro or C₁ -C₄ haloalkyl, R¹ and R² independentlyare C₁ -C₆ alkyl or phenyl; or R¹ and R² together from a saturated ringwith the nitrogen to which they are attached having 3-8 carbon atoms,optionally substituted with one or two methyl groups.
 9. The method ofclaim 8 wherein R is C₃ -C₅ alkyl R¹ is C₁ -C₄ alkyl and R² is C₁ -C₄alkyl.
 10. The method of claim 8 wherein R is isopropyl, R¹ is methyland R² is methyl.
 11. The method of claim 8 wherein R is isopropyl, R¹is methyl and R² is methyl.
 12. The method of claim 8 wherein R isisopropyl, R¹ is isobutyl and R² is isobutyl.
 13. The method of claim 8wherein R is isopropyl, R¹ and R² together are butylene.
 14. The methodof claim 8 wherien R is isopropyl, R¹ is methyl and R² is phenyl.